I could be wrong Sue but I think that it is most common for FTD to start before the ALS.

Cognitive decline in a smaller way that isn't truly what would be classed a dementia often happens later in ALS.

My Chris showed behavioural changes that I noticed about a year before his speech started slurring. Even though I always say he was rapid progression, he did have a few years of odd symptoms that were vague and fairly mild (compared to what came later).
It was like both his behavioural and physical symptoms were lower level and slowly progressing for those first years, then it was almost like a tipping point was reached and everything started to go very fast from that point on.